The amplitude ratio, PP/P, as recorded by Galitzin seismographs*

1943 ◽  
Vol 33 (3) ◽  
pp. 149-195
Author(s):  
Alexis I. Mei
Keyword(s):  
Amplitude Ratio ◽  
Angle Of Incidence ◽  
Surface Layers ◽  
P Waves ◽  
Direct Wave ◽  
Longitudinal Waves ◽  
The Earth ◽  
The Pacific ◽  
The Pacific Ocean ◽  
The Waves

Abstract The ratio of the amplitude of the longitudinal wave reflected at the surface of the earth to that of the direct wave as recorded by Galitzin seismographs was examined to find whether it might be used as a means of distinguishing between Pacific and continental reflections. Theoretically, assuming that equal energy is radiated in all directions from the source, the amplitude ratio, PP/P, for Pacific reflections should be smaller than for continental reflections at all epicentral distances, if the speed of P waves near the surface is higher under the Pacific than under the continents. The records of 194 earthquakes with epicenters at distances from 19° to 103°, and having reflections under the continents or the Pacific Ocean, were examined for the purpose. No such pattern as expected by theory was observed; on the contrary there resulted a general scattering when these ratios were plotted, for both types of reflection, against epicentral distances. The observed values of the apparent angle of incidence agreed better with those calculated for V = 8.00 km/sec. than with those for V = 6.00 km/sec., where V is the velocity of P waves near the surface of the earth. Since 8.00 km/sec. is the velocity of longitudinal waves below the surface layers of the continents, while 6.00 km/sec. is an intermediate velocity within the layers, it was concluded that the waves recorded by the Galitzin seismographs were not refracted into the surface layers of the earth and consequently that the amplitudes of waves of the periods recorded on Galitzin seismographs (4 sec. to 12 sec.) do not afford a means of differentiating between reflections at a layered surface such as the continent and at an unlayered surface such as Gutenberg considers the Pacific to be. However, comparison of some twenty records of the vertical Benioff seismograph of approximately 0.7 sec. free period (recorded waves of periods 1 sec. to 2 sec.) with those of the same earthquakes recorded by the Galitzins of 12 sec. free period showed no essentially different behavior. It was observed that the Berkeley, California, and Florissant, Missouri, stations, both using Galitzin instruments of nearly the same constants, were situated at the same distances from eight Mexican epicenters, and both received impulses from these earthquakes over the same kind of continental paths. An examination of their respective values of PP/P showed this to be larger at one station or another according as the first recorded motion at Berkeley was a condensation or a rarefaction. This variation in the values of PP/P shows that energy is not sent out equally in all directions from the source, as was assumed, and therefore that the mechanism at the focus plays an important part in the value of this ratio.

Angle of incidence and amplitude ratio of P and PP waves

1964 ◽  
Vol 54 (1) ◽  
pp. 105-121
Author(s):  
Basil Papazachos
Keyword(s):  
Atlantic Ocean ◽  
Amplitude Ratio ◽  
Angle Of Incidence ◽  
Amplitude Ratios ◽  
Crustal Layer ◽  
Longitudinal Waves ◽  
Long Period ◽  
The Earth ◽  
Incident Waves ◽  
Theoretical Results

abstract Apparent angles of incidence and amplitudes of P and PP waves of period 7 to 15 seconds were obtained from seismograms of the long period Columbia-Sprengnether instruments at the stations Manhattan (Kansas), Rolla (Missouri), Dubuque (Iowa) and Bloomington (Indiana). The calculated angle of incidence, by assuming Poisson's ratio equal to 14, agrees with a velocity of 6.4 km/sec for these longitudinal waves near the surface of the earth. The amplitude ratios of reflected to incident waves at the points half the distance between epicenters and stations were calculated. Comparison of these ratios with theoretical results shows that the unsymmetrical radiation at foci and errors in measurements make difficult, but not impossible, the use of these ratios for studying the structure of the earth. Another possible way to use the relative amplitudes of P and PP waves for studying regions of doubtful structure is to examine if those regions give reflections not only at the surface of the earth but also at the bottom of a possible crustal layer. Atlantic reflections indicate that these longitudinal waves are not affected by any surface crustal layer under the Atlantic Ocean.

Near earthquakes in Central California*

1939 ◽  
Vol 29 (3) ◽  
pp. 427-462 ◽  
Author(s):  
Perry Byerly
Keyword(s):  
Least Squares ◽  
Travel Time ◽  
Sierra Nevada ◽  
Accurate Determination ◽  
Depth Of Focus ◽  
Surface Layers ◽  
P Waves ◽  
Central California ◽  
The Waves

Summary Least-squares adjustments of observations of waves of the P groups at central and southern California stations are used to obtain the speeds of various waves. Only observations made to tenths of a second are used. It is assumed that the waves have a common velocity for all earthquakes. But the time intercepts of the travel-time curves are allowed to be different for different shocks. The speed of P̄ is found to be 5.61 km/sec.±0.05. The speed for S̄ (founded on fewer data) is 3.26 km/sec. ± 0.09. There are slight differences in the epicenters located by the use of P̄ and S̄ which may or may not be significant. It is suggested that P̄ and S̄ may be released from different foci. The speed of Pn, the wave in the top of the mantle, is 8.02 km/sec. ± 0.05. Intermediate P waves of speeds 6.72 km/sec. ± 0.02 and 7.24 km/sec. ± 0.04 are observed. Only the former has a time intercept which allows a consistent computation of structure when considered a layer wave. For the Berkeley earthquake of March 8, 1937, the accurate determination of depth of focus was possible. This enabled a determination of layering of the earth's crust. The result was about 9 km. of granite over 23 km. of a medium of speed 6.72 km/sec. Underneath these two layers is the mantle of speed 8.02 km/sec. The data from other shocks centering south of Berkeley would not fit this structure, but an assumption of the thickening of the granite southerly brought all into agreement. The earthquakes discussed show a lag of Pn as it passes under the Sierra Nevada. This has been observed before. A reconsideration of the Pn data of the Nevada earthquake of December 20, 1932, together with the data mentioned above, leads to the conclusion that the root of the mountain mass projects into the mantle beneath the surface layers by an amount between 6 and 41 km.

2. The peopling of the earth

2015 ◽  
pp. 12-28
Author(s):  
Stewart A. Weaver
Keyword(s):  
Pacific Ocean ◽  
East Africa ◽  
Cultural Exchange ◽  
Homo Erectus ◽  
The Earth ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Rift Valleys

When did exploration begin and who were the first explorers? ‘The peopling of the earth ’ shows that the deep origins of exploration are inseparable from the long process of the peopling of the earth that began between one and two million years ago, with the migration of Homo erectus out of the East Africa rift valleys. It considers the Polynesian seafaring people whose remarkable exploratory oceanic migration resulted in settlements and cultural exchange around and across the Pacific Ocean. The maritime exploration of the Norse reached Iceland, Greenland, and Newfoundland. The global circle of humanity closed, and the first of history's two big stories, that of human divergence, ended, and the second, that of human convergence, began.

A Royal Society appointment with Venus in 1769: the voyage of Cook and Banks in the Endeavour In 1768-1771 and its botanical results

1969 ◽  
Vol 24 (1) ◽  
pp. 64-90 ◽  
Keyword(s):  
Pacific Ocean ◽  
Royal Society ◽  
The Sun ◽  
Royal Navy ◽  
The Earth ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Set Up ◽  
George Iii ◽  
Made In

A little over two hundred years ago a number of serious and learned men in Copenhagen, London, Paris, St Petersbourg, Stockholm and elsewhere, men who were academicians, Fellows of the Royal Society, Lords of the Admiralty, politicians and the like, had been thinking seriously and learnedly about the behaviour of Venus, not, of course, about Venus as represented coldly and chastely by the marble statues being imported from Italy or more warmly in the paintings of Boucher and his contemporaries, but about her far distant planet which was calculated to pass across the disk of the Sun in 1769 and not to make another such transit until 1874. Observations of the 1769 transit at widely separated stations would provide, it was hoped, the means of calculating the distance of the Earth from the Sun. The Royal Society in London, having set up in November 1767 a sub-committee ‘to consider the places proper to observe the coming Transit of Venus’ and other particulars relevant to the same, presented a memorial to King George III outlining possible benefits to science and navigation from observations made in the Pacific Ocean and received in return the promise of £4000 and a suitable ship provided by the Royal Navy (8).

Geothermal

2020 ◽  
pp. 363-402
Author(s):  
Paul F. Meier
Keyword(s):  
Pacific Ocean ◽  
Geothermal Energy ◽  
Power Plants ◽  
Hot Water ◽  
Geothermal System ◽  
Enhanced Geothermal System ◽  
Heating And Cooling ◽  
The Earth ◽  
The Pacific ◽  
The Pacific Ocean

Geothermal energy is heat taken from below the surface of the earth in the form of either steam or hot water. This energy can be used to generate electricity, but also has use in heating and cooling homes and some direct uses, such as gold mining, food dehydration, and milk pasteurizing. There are four basic types of geothermal power plants including steam, flash, binary, and enhanced geothermal system (EGS). The first three rely on permeable aquifers that have water flowing through them such that hot water or steam can be extracted. EGS, however, extracts heat from deep in the earth by injecting water and creating artificial fractures in the rock. A great deal of the world’s potential for geothermal energy exists in the so-called Ring of Fire, a ring of volcanoes around the Pacific Ocean.

scholarly journals DIRECTIONAL SPECTRA FROM WAVE-GAGE ARRAYS

1970 ◽  
Vol 1 (12) ◽  
pp. 8 ◽  
Author(s):  
N.N. Panicker ◽  
L.E. Borgman
Keyword(s):  
Analytical Procedure ◽  
Wind Waves ◽  
Random Phase ◽  
Laboratory Data ◽  
Simulated Data ◽  
Phase Method ◽  
Directional Spectrum ◽  
The Pacific ◽  
The Pacific Ocean ◽  
The Waves

The ocean surface may be considered to be composed of many waves traveling at different directions with different frequencies A graphical plot showing the allocation of wave energy to the different component frequencies and directions is the directional spectrum Directional spectrum has many applications in Coastal Engineering Herein an analytical procedure is developed to obtain the directional spectrum from records of an array of wave gages The two methods developed are the "locked phase method" and the "random phase method The locked phase method can be used to obtain the distribution of both phase as well as energy of the waves with respect to frequency and direction and is a deterministic approach The random phase analysis, on the other hand, is more suitable for wind waves in the ocean and yields just the distribution of energy alone as in most other procedures of spectrum analysis The procedures programmed for computers are checked using simulated data and laboratory data Wave records of the Pacific Ocean obtained off Point Mugu, California, on a 5-gage array were analyzed using the method developed and examples of the directional spectra obtained are presented.

scholarly journals STATISTICAL AND SPECTRAL CHARACTERISTICS OF THE 2011 EAST JAPAN TSUNAMI SIGNAL IN ARRAIAL DO CABO, RJ, BRAZIL

2014 ◽  
Vol 32 (2) ◽  
pp. 235 ◽  
Author(s):  
Rogério Neder Candella
Keyword(s):  
Spectral Characteristics ◽  
Drake Passage ◽  
Tsunami Source ◽  
Brazilian Coast ◽  
South American ◽  
Signal Attenuation ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Tsunami Signal ◽  
The Waves

ABSTRACT. For the second time, the sign of a tsunami could be measured in Brazil. The waves generated by the Mw 9.0 earthquake in Japan on March 11, 2011,have spread across the Pacific Ocean and through Drake Passage reached the Atlantic Ocean, being recorded by at least three tide gauges. During the 2004 Sumatraevent, the positioning of the tsunami source allowed the waves to propagate almost directly to the South American coast and the signal was recorded at many sites ofthe Argentinian, Uruguayan and Brazilian coast. This time, the path of the waves was much more complex, causing strong signal attenuation and making difficult thedetection of the waves. Nevertheless, the tsunami signal was identified at Arraial do Cabo, RJ, mainly due to the low background noise level. This far-field record wasused to estimate statistical and spectral characteristics of arriving tsunami waves.Keywords: Japan tsunami, signal detection, Brazil. RESUMO. Pela segunda vez, o sinal de um tsunami pôde ser registrado no Brasil. As ondas originadas pelo terremoto de magnitude 9,0 ocorrido no Japão, em 11 de março de 2011, se propagaram através do oceano Pacífico e, passando pelo Estreito de Drake, atingiram o oceano Atlântico, sendo registradas por, pelo menos, três marégrafos. No evento de 2004, a posição da fonte do tsunami permitiu a propagação quase direta das ondas até a costa sul americana e o sinal pôde ser registrado emdiversos pontos na Argentina, Uruguai e Brasil. Dessa vez, o caminho das oscilações foi bem mais complexo, provocando forte atenuação do sinal e, assim, dificultandosua detecção. Apesar disso, foi possível detectar esse sinal em Arraial do Cabo, RJ, principalmente devido ao baixo nível de ruído de fundo no registro do nível do mar. O registro desses dados de campo distante foi utilizado para extrair características estatísticas e espectrais dos dados coletados.Palavras-chave: tsunami do Japão, detecção do sinal, Brasil.

scholarly journals An Indo-Pacific see-saw wobbles the Earth at intraseasonal timescales

2020 ◽  
Author(s):  
M Afroosa ◽  
B Rohith ◽  
Arya Paul ◽  
Fabien Durand ◽  
Romain Bourdallé-Badie ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Indian Ocean ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Global Scale ◽  
Pacific Basin ◽  
The Earth ◽  
The Pacific ◽  
The Pacific Ocean

Abstract Strong large-scale winds can relay their energy to the ocean bottom and elicit an almost immediate intraseasonal barotropic (depth independent) response in the ocean. The intense winds associated with the Madden-Julian Oscillation (MJO), over the tropical interface between the Indian Ocean and the Pacific Ocean (popularly known as Maritime Continent) generate significant basin-wide intraseasonal barotropic sea level variability in the tropical Indian Ocean. Here we show, using an ocean general circulation model and a network of in-situ bottom pressure recorders, that the concerted barotropic response of the Indian and the Pacific Ocean to these winds leads to an intraseasonal see-saw of oceanic mass in the Indo-Pacific basin. This global-scale mass shift is unexpectedly fast, as we show that the mass field of the entire Indo-Pacific basin is dynamically adjusted to MJO in a few days. We also explain how this near-global-scale MJO-induced oceanic phenomenon is the first signature from a climate mode that can be isolated into the Earth polar axis motion, in particular during the strong see-saw of early 2013.

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